use strict;
use warnings;
use Data::Dumper;
use Carp;

# Note: you could do extra manual checking of function arguments.
# Not necessarily recommended: shown for educational purposes.
# In example below, test_function takes exactly one argument, a ref to an ARRAY

sub test_function {
    my $narg = @_;
    $narg == 1 or croak "oops: this function takes exactly one argument, a ref to an array (you provided $narg arguments)";
    my $ref = shift;
    defined($ref) or croak "oops: argument is undef";
    my $reftype = ref($ref);
    $reftype eq '' and croak "oops: argument should be a reference";
    $reftype eq 'ARRAY' or croak "oops: argument should be ARRAY ref (not a '$reftype' ref)";
    warn "reftype='$reftype'\n";
    # Note: next line will die with "Not an ARRAY reference error" if $ref is not an ARRAY ref
    warn "num elts=", scalar(@$ref), "\n";

    # ... function body, process array ref $ref ...
    print Dumper($ref);
}

my @test_array = ([1, 2, 3], [4, 5, 6]);
my %test_hash = ( "one" => 1, "two" => 2 );

# Can test function being called with invalid arguments...
# test_function();                   # oops, no arguments
# test_function(undef);              # oops, passed undef
# test_function( \@test_array, 2 );  # oops, two arguments
# test_function(1);                  # oops, one argument but not a ref
# test_function( @test_array );      # oops, array (not array ref)
# test_function( \%test_hash );      # oops, hash ref (not array ref)

test_function( \@test_array );       # Correct! One argument, array ref!